The present invention relates to in instrument for measuring two-dimensional light images which are repeated at ultra-high speed, and especially to an instrument for concurrently measuring two-dimensional multichannel light images which may change at ultra-high speed, i.e., the time-resolving spectroscopic measurement of fluorescence stimulated by a laser pulse, or spatial time-resolving measurements in the pico second range.
The streaking camera is used as an instrument to observe an optical intensity distribution changing at high speed.
The streaking tube used in the streak camera is an electron tube wherein a pair of deflection electrodes are arranged in a space between the photocathode and phosphor layer.
When the light pulse in incident on the photocathode of the streaking tube, the photocathode emits photoelectrons.
If an electric field is applied across the pair of deflection electrodes while the photoelectrons move toward the phosphor layer, the incident light intensity change can be detected on the phosphor layer as a linear light intensity distribution along the sweeping trace on the phosphor screen (in the direction of scanning with time).
This light intensity distribution is called a streaking image.
The streak camera consists of a streaking tube, an optical system to project the light pulse to be measured onto the photocathode of the streaking tube, and a power supply to feed the supply voltage to the streaking tube.
High-repetition-rate pulse light measuring instruments (Japanese Patent Application Laid-Open Nos. 104519/1984 and 135330/1984) and an electron tube device for the high-repetition-rate pulse light measuring instruments (Japanese Patent Application Laid-Open No. 134538/1984) have already been proposed, and these instruments and device apply to the light emitted at high repetition rate in accordance with the principle of operation of the streaking tube aforementioned.
These are suitable for measuring the extremely low intensity light changing with time at a high repetition rate. Data arranged on the streaking tube in a direction perpendicular to the sweeping of the streaking tube cannot be output at the same time. That is, data on a plurality of channels cannot be output concurrently.
The streaking image on the phosphor layer of the streaking tube can be analyzed by picking it up on the television camera.
Highly repetitive streak images can be superimposed during one frame time (1/30 or 1/60 sec.) and this is picked up by the television camera. Therefore, an image signal with greater level can be obtained.
The dynamic range, however, is limited to a value much lower than 10.sup.4 to 10.sup.6 because of the following four reasons:
First, the image is stored as charges in the target capacitance of the pick up tube and the dynamic range of an image for one field period is of the order of 100 to 1.
Second, charges caused by the dark current of the pick up tube are stored during the above one field and the measurement accuracy of faint streaking images is low.
Third, the dynamic range of the streaking image for a plurality of fields is also limited to 1000:1 by both the target capacitance and dark current.
The dynamic range of the streaking image can be improved by feeding the streaking tube output to a photomultiplier tube when such an electron tube device for measuring the high-speed light pulses as disclosed in Japanese Patent Application Laid-Open No. 134538/1984 is used. The streaking images on a plurality of channels, however, cannot concurrently be measured.
The streaking images on a plurality of channels can only be measured in sequence, and this lengthens the measuring time.
The objective of the present invention is to provide an instrument for measuring a two-dimensional light image repetitively appearing at ultra-high speed, i.e., an instrument for the time-resolving spectroscopic measurement of fluorescence stimulated by a laser pulse, or an instrument for spatial time-resolving measurements in the pico second region.